Nymphaea caerulea, known primarily as blue lotus (or blue Egyptian lotus), but also blue water lily (or blue Egyptian water lily), and sacred blue lily (or sacred narcotic lily of the Nile), is a water lily in the genusNymphaea. Like other species in the genus, the plant contains the psychoactive alkaloid apomorphine. It was known to the Mayan and Ancient Egyptian civilizations.

The leaves are broadly rounded, 25–40 cm (10–16 in) across, with a notch at the leaf stem. The flowers are 10–15 cm (4–6 in) in diameter.

Reports in the literature by persons unfamiliar with its actual growth and blooming cycle have suggested that the flowers open in the morning, rising to the surface of the water, then close and sink at dusk.[citation needed] In fact, the flower buds rise to the surface over a period of two to three days, and when ready, open around 9:30 am and close about 3:00 pm. The flowers and buds do not rise above the water in the morning, nor do they submerge at night. The flowers have pale bluish-white to sky-blue or mauvepetals, smoothly changing to a pale yellow in the centre of the flower.

Along with the white lotus, Nymphaea lotus are also native to Egypt. The plant and flower are very frequently depicted in Egyptian art. They have been depicted in numerous stone carvings and paintings, including the walls of the famous temple of Karnak, and are frequently depicted in connection with "party scenes", dancing or in significant spiritual or magical rites such as the rite of passage into the afterlife. N. caerulea was considered extremely significant in Egyptian mythology, regarded as a symbol of the sun, since the flowers are closed at night and open again in the morning. At Heliopolis, the origin of the world was taught to have been when the sun god Ra emerged from a lotus flower growing in "primordial waters". At night, he was believed to retreat into the flower again.[2] Due to its colour, it was identified, in some beliefs, as having been the original container, in a similar manner to an egg, of Atum, and in similar beliefs Ra, both solar deities. As such, its properties form the origin of the "lotus variant" of the Ogdoadcosmogeny. It was the symbol of the Egyptian deity Nefertem.[3]

N. caerulea is illegal in Latvia since November 2009. It is schedule 1 drug. Possession of quantities up to 1 gram are fined up to 280 euros, for second offences within a year period criminal charges are applied. Possession of larger quantities can be punished by up to 15 years in prison.[5]